Stable pharmaceutical formulations of methylnaltrexone

ABSTRACT

Stable pharmaceutical compositions useful for administering methylnaltrexone are described, as are methods for making the same. Kits, including these pharmaceutical compositions, also are provided.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/639,892, filed on Dec. 16, 2009, which is a continuation ofU.S. patent application Ser. No. 10/821,811, filed on Apr. 8, 2004,which claims priority to U.S. Provisional Application No. 60/461,611,filed Apr. 8, 2003, the entire contents of each of which are herebyincorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to methylnaltrexone pharmaceutical preparations,methylnaltrexone formulations, methylnaltrexone kits, and methods ofmaking the same.

BACKGROUND OF THE INVENTION

Quaternary amine opioid antagonist derivatives have been shown to haveutility in a number of contexts. They are considered peripherally actingonly, and, therefore, find particular utility in reducing theside-effects of opioids without reducing the analgesic effect ofopioids. Such side effects include nausea, emesis, dysphoria, pruritis,urinary retention, bowel hypomotility, constipation, gastrichypomotility, delayed gastric emptying and immune suppression. Theutility of these peripherally acting opioid antagonists is not limitedto reducing side-effects stemming from opioid analgesic treatment.Instead, these derivatives also have utility in circumstances whereendogenous opioids alone (or in conjunction with exogenous opioidtreatment) cause undesirable conditions such as ileus and other suchconditions including, but not limited to, those mentioned above.

Methylnaltrexone is a quaternary amine opioid antagonist derivative,discovered in the mid-70s. Methylnaltrexone and some of its uses aredescribed in U.S. Pat. Nos. 4,176,186, 4,719,215, 4,861,781, 5,102,887,5,972,954, and 6,274,591. Stable formulations of methylnaltrexone,however, have heretofore not existed. Methylnaltrexone apparently wasassumed to have a structure that was inherently stable. The stability ofa pharmaceutical composition in solution, however, is not necessarilypredictable either over time when stored at room temperature or whenautoclaved.

Naloxone is an opioid antagonist that acts both centrally andperipherally. It differs structurally from methylnaltrexone and would beexpected to have a different stability in solution. An allegedly stableformulation of naloxone is described in U.S. Pat. No. 5,866,154.

Surprisingly, it has been discovered that methylnaltrexone is unusuallyunstable. It further has been discovered that methylnaltrexone hascertain degradation products different from those of naloxone. It alsohas been discovered that critical parameters and conditions are requiredfor stable formulations of methylnaltrexone.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a composition or preparation thatis a solution of methylnaltrexone or a salt thereof, wherein thepreparation after autoclaving has a concentration of methylnaltrexonedegradation products that does not exceed 2% of the methylnaltrexone orsalt thereof in the preparation. Preferably, the concentration of suchdegradation products does not exceed 1.5%, 1%, 0.5%, 0.25%, or even0.125% of the methylnaltrexone or salt thereof in the preparation. Thecomposition or preparation can contain one of, any combination of, orall of a chelating agent, a buffering agent, an anti-oxidant, acryoprotecting agent, an isotonicity agent and an opioid. The preferredchelating agent is disodium edetate or a derivative thereof. Thedisodium edetate preferably is at a concentration ranging from between0.001 and 100 mg/nal, more preferably 0.05 to 25.0 mg/ml, and even morepreferably, 0.1 to 2.5 mg/ml. A preferred buffering agent is citratebuffer. The citrate buffer typically is in a concentration ranging from0.001 to 100.0 mM, preferably from 0.1 to 10 mM, and more preferably,0.1 to 5.0 mM. A preferred cryoprotecting agent is mannitol.

The composition or preparation preferably has a pH that does not exceed4.25. More preferably, the pH ranges from 2.0 to 4.0, 3.0 to 4.0, andmost preferably, from 3.0 to 3.5.

According to another aspect of the invention, a composition orpreparation is provided, which includes a solution of methylnaltrexoneor a salt thereof, wherein the preparation after storage at about roomtemperature for six months has a concentration of methylnaltrexonedegradation products that does not exceed 2% of the methylnaltrexone inthe preparation. The concentration of the methylnaltrexone degradationproducts preferably does not exceed 1.5%, 1.0%, 0.5%, 0.25%, and even0.125% of the methylnaltrexone in the preparation. The composition orpreparation can contain one of, any combination of, or all of achelating agent, a buffering agent, an anti-oxidant, a cryoprotectingagent, an isotonicity agent and an opioid. The preferred chelating agentand concentrations are as described above. The preferred buffering agentand concentrations are as described above. Preferably, the compositionor preparation has a pH that does not exceed 4.25. The preferred pHs andranges are as described above.

According to another aspect of the invention, a stable composition orpreparation is provided. The composition or preparation is a solution ofmethylnaltrexone or a salt thereof wherein the pH is below 4.25.Preferably, the pH is between 2.75 and 4.25, more preferably, between3.0 and 4.0, and most preferably, between 3.0 and 3.5. According toconventional procedures, pH can be adjusted with an acid. Examples ofacids useful for this purpose include hydrochloric acid, citric acid,sulfuric acid, acetic acid, and phosphoric acid. The stable compositionor preparation can also include any one of, any combination of, or allof a chelating agent, a buffering agent, an isotonicity agent, anantioxidant, a cryogenic agent, and an opioid.

According to another aspect of the invention, a stable composition orpreparation is provided. The composition or preparation is a solution ofmethylnaltrexone or salt thereof, wherein the solution further comprisesa chelating agent in an amount sufficient to inhibit degradation of themethylnaltrexone or salt thereof, whereby the amount is such that thecomposition or preparation after autoclaving has a concentration ofmethylnaltrexone degradation products that does not exceed 0.5%, 0.25%or even 0.125% of the methylnaltrexone or salt thereof in thecomposition or preparation. The composition or preparation can furtherinclude any one of, any combination of, or all of a buffering agent, anisotonicity agent, an antioxidant and an opioid. Preferred chelatingagents, buffering agents and pHs are as described above.

According to another aspect of the invention, a composition orpreparation is provided. The composition or preparation is a solution ofmethylnaltrexone or salt thereof in at least one methylnaltrexonedegradation inhibiting agent. The agent can be any one of, anycombination of, or all of a chelating agent, a buffering agent, and anantioxidant, provided that the solution has a pH ranging from 2.0 to6.0. The degradation inhibiting agent is present in an amount sufficientto render the composition or preparation stable, wherein the compositionor preparation is processed under at least one sterilization technique,and wherein the composition or preparation is substantially free ofmethylnaltrexone degradation products. The composition or preparationcan be stable to storage for at least six months, at least twelvemonths, or at least twenty-four months, at about room temperature.Preferably, the composition or preparation is stable after autoclaving.The composition or preparation further may include either or both of anisotonicity agent and an opioid. Preferably, the pH of the solution isbetween 2.75 and 4.25, more preferably, between 3.0 and 4.0, and mostpreferably, between 3.0 and 3.5.

In any one of the foregoing aspects of the invention, the composition orpreparation can be a pharmaceutical composition.

In any one of the foregoing aspects of the invention, themethylnaltrexone can be present in a therapeutically effective amount.In some embodiments, the concentration of methylnaltrexone ranges from0.01 to 100 mg/ml. In other embodiments, the methylnaltrexoneconcentration ranges between 0.1 and 100.0 mg/ml. In other embodiments,the methylnaltrexone ranges between 1.0 and 50.0 mg/ml.

In any one of the foregoing embodiments, the methylnaltrexone can bepresent in an amount sufficient to treat nausea, emesis, dysphoria,pruritus, urinary retention, ileus, post-operative ileus, post-partumileus, paralytic ileus, bowel hypomotility, constipation, gastrichypomotility, delayed gastric emptying, decreased biliary secretion,decreased pancreatic secretion, biliary spasm, increased sphincter tone,cutaneous flushing, impaction, sweating, inhibition of gastrointestinalmotility, inhibition of gastric emptying, gastrointestinal dysfunction,incomplete evacuation, bloating, abdominal distention, increasedgastroesophageal reflux, hypotension, bradycardia, irritable bowelsyndrome, or immunosuppression.

In any of the foregoing embodiments, the methylnaltrexone can be presentin an amount sufficient to accelerate discharge from hospitalpost-surgery (including abdominal surgeries such as rectal resection,colectomy, stomach, esophageal, duodenal, appendectomy, hysterectomy, ornon-abdominal surgeries such as orthopedic, trauma injuries, thoracic ortransplantation), for example, by accelerating bowel sounds aftersurgery, or speeding the time to first food intake or first bowelmovement. In other important embodiments, the amount is sufficient toinduce taxation. This has particular application where the subject is achronic opioid user.

In any one of the foregoing embodiments, the solution ofmethylnaltrexone or salt thereof may be contained in a sealed containersuch as a bottle, an infusion bag, a syringe, a vial, a vial with aseptum, an ampoule, an ampoule with a septum, or a syringe. Thecontainer may include indicia indicating that the solution has beenautoclaved or otherwise subjected to a sterilization technique.

According to another aspect of the invention, any of the foregoingembodiments is lyophilized, preferably in the presence of acryoprotecting agent. The invention therefore provides a lyophilizedpreparation of methylnaltrexone. Preferably, the lyophilized preparationis a stable preparation, containing less than 1%, less than 0.5%, lessthan 0.25% and even less than 0.125% methylnaltrexone degradationproduct. The preparation can contain a cryoprotecting agent, whichpreferably is neutral or acidic in water.

According to another aspect of the invention, a product is provided. Theproduct is a stable lyophilized formulation of methylnaltrexone, whereinthe formulation upon reconstitution and water at a concentration of 20mg/ml has a pH of between 2 and 6. In some embodiments, the formulationupon reconstitution has a pH of about 2, about 3, about 4, about 5, orabout 6. The formulation can include a cryoprotecting agent present inamounts sufficient to render the formulation stable. The cryoprotectingagent in important embodiments are polymerized carbohydrates. Apreferred cryoprotecting agent is mannitol. Any one of the foregoingsolutions described above can be lyophilized. It therefore is an aspectof the invention that such materials include one or any combination of abuffering agent, a chelating agent, an antioxidant, and an isotonicityagent. Preferred materials are as described above.

According to still another aspect of the invention, a product isprovided that includes methylnaltrexone and the degradation inhibitingagent selected from the group consisting of a chelating agent, abuffering agent, an antioxidant, and combinations thereof, wherein thedegradation inhibiting agent is present in an amount sufficient torender stable the solution of the product containing a concentration of20 mg/ml methylnaltrexone in water. Preferably, the product when insolution at a concentration of 20 mg/ml methylnaltrexone yields a pH ofbetween 2 and 6.

According to another aspect of the invention, a pharmaceuticalpreparation is provided. The pharmaceutical preparation containsmethylnaltrexone, sodium chloride, citric acid, trisodium citrate, anddisodium edetate. In one important embodiment, the methyl naltrexone ispresent between 20 and 40 mg/ml, the sodium chloride is present between2 and 6 mg/ml, the citric acid is present between 0.05 and 0.1 mg/ml,the trisodium citrate is present between 0.025 and 0.075 mg/ml, and thedisodium edetate is present between 0.5 and 1.0 mg/ml.

The buffering agent may be any pharmaceutically acceptable bufferingagent. Common buffering agents include citric acid, sodium citrate,sodium acetate, acetic acid, sodium phosphate and phosphoric acid,sodium ascorbate, tartaric acid, maleic acid, glycine, sodium lactate,lactic acid, ascorbic acid, imidazole, sodium bicarbonate and carbonicacid, sodium succinate and succinic acid, histidine, and sodium benzoateand benzoic acid. The preferred buffering agent is a citrate bufferingagent.

The chelating agent may be any pharmaceutically acceptable chelatingagent. Common chelating agents include ethylenediaminetetraacetic acid(EDTA) and derivatives thereof, citric acid and derivatives thereof,niacinamide and derivatives thereof, and sodium desoxycholate andderivatives thereof. The preferred chelating agent is disodium edetate.

The antioxidant may be any pharmaceutically acceptable antioxidant.Common antioxidants include those selected from the group consisting ofan ascorbic acid derivative, butylated hydroxy anisole, butylatedhydroxy toluene, alkyl gallate, sodium meta-bisulfite, sodium bisulfite,sodium dithionite, sodium thioglycollic acid, sodium formaldehydesulfoxylate, tocopherol and derivatives thereof, monothioglycerol, andsodium sulfite. The preferred antioxidant is monothioglycerol.

The cryoprotecting agent may be any pharmaceutically acceptablecryoprotecting agent. Common cryoprotecting agents include histidine,polyethylene glycol, polyvinyl pyrrolidine, lactose, sucrose, andmannitol. Improtant cryoprotecting agents are polyols. The preferredcryoprotecting agent of the invention is mannitol.

The opioid can be any pharmaceutically acceptable opioid. Common opioidsare those selected from the group consisting of alfentanil, anileridine,asimadoline, bremazocine, burprenorphine, butorphanol, codeine,dezocine, diacetylmorphine (heroin), dihydrocodeine, diphenoxylate,fedotozine, fentanyl, funaltrexamine, hydrocodone, hydromorphone,levallorphan, levomethadyl acetate, levorphanol, loperamide, meperidine(pethidine), methadone, morphine, morphine-6-glucoronide, nalbuphine,nalorphine, opium, oxycodone, oxymorphone, pentazocine, propiram,propoxyphene, remifentanyl, sufentanil, tilidine, trimebutine, andtramadol.

The isotonicity agent can be any pharmaceutically acceptable isotonicityagent. Common isotonicity agents include those selected from the groupconsisting of sodium chloride, mannitol, lactose, dextrose, glycerol,and sorbitol. The preferred isotonicity agent is mannitol.

The pharmaceutical preparation may optionally comprise a preservative.Common preservatives include those selected from the group consisting ofchlorobutanol, parabens, thimerosol, benzyl alcohol, and phenol.

According to another aspect of the invention, a method is provided forpreparing an autoclaved preparation of a solution of methylnaltrexone orsalts thereof, whereby the autoclaved preparation has a concentration ofmethylnaltrexone degradation products that does not exceed 2% of themethylnaltrexone or salt thereof in the preparation. The method involvesproviding a solution, having a pH of 4.25 or less, of methylnaltrexoneor a salt thereof, and being substantially free of methylnaltrexonedegradation products, and autoclaving the solution. The solution cancontain, optionally, any one of, any combination of, or all of achelating agent, an isotonicity agent, a buffering agent, anantioxidant, a cryoprotecting agent, and an opioid. Preferably, the pHof the solution ranges from 2.0 to 4.0. More preferably, from 3.0 to4.0, and most preferably from 3.0 to 3.5. Preferred chelating agents,isotonicity agents, buffering agents, antioxidants, cryoprotectingagents, and opioids are as described above. Preferred concentrations ofmethylnaltrexone, likewise, are as described above.

According to another aspect of the invention, a method is provided forpreparing an autoclaved preparation. The preparation has a concentrationof methylnaltrexone degradation products that does not exceed 2% of themethylnaltrexone or salt thereof in the preparation. The method involvesproviding a solution containing methylnaltrexone or salt thereof and achelating agent, the solution being substantially free ofmethylnaltrexone degradation products, and then autoclaving thesolution. The chelating agent is present in an amount sufficient toprotect the preparation against substantial unwanted degradation ofmethylnaltrexone or its salt, and maintain the solution to besubstantially free of methylnaltrexone degradation products. Preferredchelating agents and concentrations thereof are as described above. Thepreparation may include, optionally, any one of, any combination of, orall of a buffering agent, an isotonicity agent, an antioxidant, acryoprotecting agent, and an opioid. Preferred buffering agents,isotonicity agents, antioxidants and opioids, as well as concentrations,are as described above. Preferred pHs of the solution likewise are asdescribed above. Preferably, the degradation products after autoclavingdo not exceed 1.5%, 1%, 0.5%, 0.25% or even 0.125%.

According to another aspect of the invention, a method is provided forinhibiting the formation of methylnaltrexone degradation products in apreparation that is a solution of methylnaltrexone or salts thereof. Themethod involves preparing an aqueous solution containing at least onemethylnaltrexone degradation inhibiting agent selected from the groupconsisting of a chelating agent, a buffering agent, an antioxidant, acryoprotecting agent, and combinations thereof. A powdered source ofmethylnaltrexone or salt thereof is dissolved into the solution to formthe preparation. The preparation has or is adjusted without addition ofa pH-adjusting base to have a pH of between 2 and 6. More preferably,the pharmaceutical preparation is adjusted to have a pH ranging from 3to 5, more preferably, 3 to 4, and most preferably, 3.0 to 3.5. Anisotonicity agent may be added to the solution. Likewise, an opioid maybe added to the solution.

In any one of the foregoing aspects of the invention, the preparationcan be a pharmaceutical preparation.

According to another aspect of the invention, a method is provided forpreparing a stable pharmaceutical preparation that is an aqueoussolution of methylnaltrexone or salts thereof to inhibit formation ofmethylnaltrexone degradation products. A solution is provided containingmethylnaltrexone or salts thereof and at least one methylnaltrexonedegradation inhibiting agent. The solution is processed under at leastone sterilization technique prior to and/or after terminal filling thesolution in a sealable container to form the stable pharmaceuticalpreparation, wherein the method is carried out without the addition ofpH-adjusting base to the solution. The methylnaltrexone degradationinhibiting agent can be selected from the group consisting of achelating agent, a buffering agent, an antioxidant, and combinationsthereof. An isotonicity agent can be added. A cryoprotecting agent canalso be added. Likewise, an opioid can be added. Preferred chelatingagents, buffering agents, antioxidants, isotonicity agents,cryoprotecting agents, and opioids are as described above. Preferredconcentrations are as described above. The solution may be processed toadjust the pH. This is preferably done using an acid. Most preferably,the solution is adjusted to a range between a pH of 2 and 6, morepreferably, between 3 and 5, 3 and 4, and most preferably between 3.0and 3.5. The material can be contained in a sealed container. Thecontainer can be purged with nitrogen and/or sparged to eliminateoxygen.

In some embodiments of the invention, parenteral formulations areprovided. In one embodiment, the formulation made by dissolvingmethylnaltrexone diluted in water, to which mannitol is added. Thesolution is then filter sterilized followed by lyophilization.Therefore, the product may be provided in lyophilized form, and incombination with certain cryoprotectants such as mannitol or lactose.Optionally, a reconstituting diluent is provided, such as aphysiological saline diluent.

According to another aspect of the invention, a kit is provided. The kitis a package containing a sealed container comprising any one of thepreparations described above, together with instructions for use. Thekit can also include a diluent container containing a pharmaceuticallyacceptable diluent. The kit can further comprise instructions for mixingthe preparation and the diluent. The diluent can be any pharmaceuticallyacceptable diluent. Well known diluents include 5% dextrose solution andphysiological saline solution. The container can be an infusion bag, asealed bottle, a vial, a vial with a septum, an ampoule, an ampoule witha septum, an infusion bag or a syringe. The kit further can contain anopioid container containing an opioid. The containers can optionallyinclude indicia indicating that the containers have been autoclaved orotherwise subjected to sterilization techniques. The kit can includeinstructions for administering the various solutions contained in thecontainers to subjects.

The invention also involves methods of treatment. According to anotheraspect of the invention, a method is provided for treating a subject inneed of such treatment with an effective amount of methylnaltrexone or asalt thereof. The method involves administering to the subject aneffective amount of methylnaltrexone or salt thereof in any one of thepharmaceutical preparations described above, detailed herein, and/or setforth in the claims. In one aspect, the method is a method forinhibiting a peripheral opioid receptor in a human subject. In anotheraspect, the method is for reducing a side-effect of opioid treatment. Inanother aspect, the method is for treating any one of a conditionselected from the group consisting of nausea, emesis, dysphoria,pruritus, urinary retention, ileus, post-operative ileus,post-partumileus, parallytic ileus, bowel hypomotility, constipation,gastric hypomotility, delayed gastric emptying, decreased biliarysecretion, decreased pancreatic secretion, biliary spasm, increasedsphincter tone, cutaneous flushing, impaction, sweating, inhibition ofgastrointestinal motility, inhibition of gastric emptying,gastrointestinal dysfunction, incomplete evacuation, bloating, abdominaldistention, increased gastroesophageal reflux, hypotension, bradycardia,irritable bowel syndrome, or immunosuppression.

In any of the foregoing embodiments, the methylnaltrexone can be presentin an amount sufficient to accelerate discharge from hospitalpost-surgery, accelerate bowel sounds after surgery, or induce laxation.

The subject can be any subject in need of such treatment. Importantsubjects include those receiving opioids including opioids for pain,cancer or surgical patients, or immunosuppressed or immunocompromisedpatients (including HIV infected patients), patients with advancedmedical illness, terminally ill patients, patients with neuropathies,patients with rheumatoid arthritis, patients with osteoarthritis,patients with chronic pack pain, patients with spinal cord injury,patients with chronic abdominal pain, patients with chronic pancreaticpain, patients with pelvic/perineal pain, patients with fibromyalgia,patients with chronic fatigue syndrome, patients with migraine ortension headaches, patients on hemodialysis, and patients with sicklecell anemia.

In the foregoing description, applicants have described the invention inconnection with methylnaltrexone or salts thereof. Such salts include,but are not limited to, bromide salts, chloride salts, iodide salts,carbonate salts, and sulfate salts. It should be understood, however,that methylnaltrexone is a member of a class of compounds known asquaternary derivatives of noroxymorphone, as disclosed in U.S. Pat. No.4,176,186, the entire disclosure of which is incorporated herein byreference. It is believed that the invention extends to any suchquaternary derivative of noroxymorphone, and the invention is intendedto embrace pharmaceutical preparations, methods and kits containing suchderivatives. Another aspect of the invention then embraces the foregoingsummary but read in each aspect as if any such derivative is substitutedwherever “methylnaltrexone” appears. Likewise, the invention alsoembraces each and every claim read as if the term “quaternary derivativeof noroxymorphone” were substituted whenever “methylnaltrexone” appears.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting methylnaltrexone degradation productseluting from a column at time zero (peak Nos. 1, 2 and 4 are degradationproducts; peak No 4 is methylnaltrexone; peak no 5. O-methylnaltrexonebromide).

FIG. 2 is a graph depicting methylnaltrexone degradation productseluting from a column at 12 months (peak Nos. 1, 2 and 4 are degradationproducts; peak No 4 is methylnaltrexone; peak no 5. O-methylnaltrexonebromide).

FIG. 3 is a schematic representation of a kit according to the inventioncontaining the formulations described herein.

DETAILED DESCRIPTION OF THE INVENTION

Applicants have discovered that during the autoclaving process,methylnaltrexone in aqueous solution tends to degrade to a surprisingextent. The amount of degradation resulting from simple autoclaving(122° C., 15 lbs. pressure for 20 min.) can be as high as 10%. Thedegradation products are depicted in FIG. 1, and appear to include atleast two predominant degradants having relative retention times (RRT)of 0.72 (2.828 minutes) and 0.89 (3.435 minutes) and, with other minorforms as can be observed. The degradant identified by the 0.72 RRT peakappears in small amounts, 0.074, immediately upon dissolving themethylnaltrexone into solution and increases overtime with storage orautoclaving 0.25%. The degradant identified by the 0.89 RRT peak appearsonly after storage over time or after autoclaving (<0.05% and 0.724%,respectively). Applicants also have discovered that methylnaltrexone isunstable in aqueous solutions when stored at room temperature or even at4° C. for significant (but commercially necessary) periods of time suchas 6 months, 12 months or even two years. Degradation occurs withoutregard to whether the aqueous solution was previously autoclaved orfilter sterilized. It would be desirable to stabilize formulations ofmethylnaltrexone such that following the autoclaving process orfollowing storage (or both autoclaving and storage), the amount of thetotal degradation products would be less than 2.0%, 1.5%, 1.0%, 0.5%,0.25%, and even 0.125%.

The invention provides stable formulations of methylnaltrexone. Bystable solutions of methylnaltrexone, it is meant that followingautoclaving at 122° C., 15 lbs. pressure for 20 minutes, themethylnaltrexone degradation products resulting from such conditions arenot more than 2% of the total methylnaltrexone present in a givensolution. By stable solution of methylnaltrexone, it also is meant thatfollowing storage of an unautoclaved solution at room temperature fortwelve months, the methylnaltrexone degradation products resulting fromsuch conditions are not more than 2% of the total methylnaltrexonepresent in a given solution. By stable solutions of methylnaltrexone, itis also meant that following storage of an unautoclaved solution at roomtemperature for two months, the methylnaltrexone degradation productsresulting from such conditions are not more than 1.0% of the totalmethylnaltrexone present in a given solution. By stable lyophilizedformulations of methylnaltrexone, it is meant that followinglyophilization and storage at room temperature of methylnaltrexone fortwo months, and their reconstitution in water the methylnaltrexonedegradation products resulting from such conditions are not more than1.0% of the total methylnaltrexone present in a given solution.

It was surprisingly discovered that pH alone can solve the problem ofexcessive methylnaltrexone degradation products. In particular, it wasdiscovered that when the pH of a methylnaltrexone solution containing 2mg/mL of methylnaltrexone was at about 4.25 pH or less, there was asteep drop-off in the amount of methylnaltrexone degradation productsfollowing autoclaving. When the pH of the solution containingmethylnaltrexone was adjusted to between 3.5 and 4.0, then the totalpercentage of degradants fell below 2%, and in certain instances evenbelow 1.39%. When the pH was adjusted to between 3.0 and 3.5, thepercentage of total degradants dropped to about 0.23% after autoclaving.It was also noted that there was a significant drop, before a plateau,when the pH of the methylnaltrexone solution was brought to below 6.0prior to autoclaving. Adjusting pHs to between 4.25 and 6 was notsufficient to produce stable formulations of methylnaltrexone (throughthe adjustment of pH alone). As will be seen below, however,manipulating other parameters in concert with pH resulted in stableformulations of methylnaltrexone anywhere in a range from a pH of 2.0 to6.0. The benefits of a low pH on the stability of methylnaltrexoneformulations persisted in the presence of chelating agents, isotonicityagents, buffering agents, and antioxidants. Thus, the invention in oneaspect provides stable formulations of methylnaltrexone in solution,wherein the pH is below 4.25, preferably between 3.0 and 4.0, and mostpreferably between 3.0 and 3.5.

Applicants also noted that despite setting the pH of a methylnaltrexonesolution at points between 3.0 and 6.0 using a pH-adjusting acid orpH-adjusting base prior to autoclaving and despite the benefits obtainedfrom lower pH, the pH of the autoclaved sample drifted almostimmediately to about 7.0. It was therefore tested, in particular,whether buffering agents could eliminate the pH drift that resulted fromautoclaving without negatively affecting the ability to protect againstheat degradation resulting from autoclaving. Applicants discovered thatbuffering agents indeed could be employed to stabilize the pH ofmethylnaltrexone solutions throughout the autoclaving process withoutpermitting degradation products to exceed acceptable minimums. Bufferswere used in concentrations ranging from 0.25 mM to 25 mM. Acceptablelevels of degradation products were obtained at all bufferconcentrations tested. It was noted, however, that citrate buffer hadproperties more desirable than those of acetate buffer. In particular,the addition of citrate buffer did not seem to alter in any materialrespects the amount of degradation products resulting from autoclavingthe methylnaltrexone solution, resulting in less than 0.23% ofdegradation products at pH of 3.5. The addition of acetate buffer,however, appeared to increase somewhat the amount of methylnaltrexonedegradation products, although not to unacceptable levels, resulting inless than 1.39% of degradation products at pH of 3.6. Nonetheless,citrate buffer surprisingly is preferable to acetate buffer. Thepreferred citrate buffer range is between about 2 and 5 mM.

Buffers in general are well known to those of ordinary skill in the art.Buffer systems include citrate buffers, acetate buffers, borate buffers,and phosphate buffers. Examples of buffers include citric acid, sodiumcitrate, sodium acetate, acetic acid, sodium phosphate and phosphoricacid, sodium ascorbate, tartartic acid, maleic acid, glycine, sodiumlactate, lactic acid, ascorbic acid, imidazole, sodium bicarbonate andcarbonic acid, sodium succinate and succinic acid, histidine, and sodiumbenzoate and benzoic acid.

Applicants also discovered, surprisingly, that a chelating agent alonewas capable of reducing the amount of degradation products to acceptablelevels. In particular, pH was not adjusted and disodium edetate wasadded at concentrations of 0.01, 0.1, 0.25, 0.5, 0.75, and 1.0 mg/mL.The disodium edetate stabilized methylnaltrexone against heatdegradation in a concentration-dependent manner. As little as 0.01 mg/mLhad a substantial effect on the amount of degradants, yieldingapproximately 2.3% total degradants. A concentration of 0.1 mg/mLresulted in under 1.5% total degradants. There was a critical point atapproximately 0.3-0.4 mg/mL where the total degradants became slightlyunder 0.5% and leveled off with increasing amounts of disodium edetate.Thus, disodium edetate alone was sufficient to render stable anunbuffered solution of methylnaltrexone with no adjustment to pH. Thiswas a surprising result.

Applicants believe that the result is not limited to disodium edetate.Instead, other chelating agents well known to those of ordinary skill inthe art will be useful according to the invention. Chelating agents arechemicals which form water soluble coordination compounds with metalions in order to trap or remove the metal irons from solution, therebyavoiding the degradative effects of the metal ions. Chelating agentsinclude ethylenediaminetetraacetic acid (also synonymous with EDTA,edetic acid, versene acid, and sequestrene), and EDTA derivatives, suchas dipotassium edetate, disodium edetate, edetate calcium disodium,sodium edetate, trisodium edetate, and potassium edetate. Otherchelating agents include citric acid and derivatives thereof. Citricacid also is known as citric acid monohydrate. Derivatives of citricacid include anhydrous citric acid and trisodiumcitrate-dihydrate. Stillother chelating agents include niacinamide and derivatives thereof andsodium desoxycholate and derivatives thereof. A synergistic effect ofpII and disodium edetate was also observed. At pH 3-3.5, in the presenceof citrate buffer (25 mM), and 0.01 mg/mL disodium edetate, the totaldegradants after autoclaving amounted to less than 0.4%. Under the sameconditions, except increasing the concentration of disodium edetate to 1mg/mL, there was no detectable difference. That is, the degradants wereon the order of approximately 0.4% after autoclaving. The circumstance,however, differed when pH was adjusted upwardly to between 6.0 and 7.0in an unbuffered system. In particular, at a pH adjusted upwardly tobetween 6.0 and 7.0, the total degradants were above 3-6% at aconcentration of 0.01 mg/mL disodium edetate and approximately 2.8% at1.0 mg/mL disodium edetate. This at first glance appears anomalous withthe results described above, where disodium edetate alone was sufficientto bring total degradants under 0.5% at concentrations aboveapproximately 0.3 disodium edetatc mg/mL. It was discovered, however,that the increase in degradation was due to the addition of apH-adjusting base to the solution containing methylnaltrexone toupwardly adjust the pH to 6.0˜7.0. Therefore, it was discoveredunexpectedly that the addition of a pH-adjusting base, such as sodiumhydroxide, to a solution containing methylnaltrexone should be avoidedin order to minimize the presence of degradants.

The same results were achieved through a combination of acetate bufferand disodium edetate at 0.01 mg/mL and 1.0 mg/mL, although, once again,citrate buffer seemed to work surprisingly better than acetate buffer inprotecting methylnaltrexone to from heat degradation. Higher levels ofdisodium edetate in the presence of acetate buffer could compensate,however, for the differential effect that was observed when usingcitrate buffer versus acetate buffer. It is to be noted that citratebuffer also is a chelating agent, which might contribute to its apparentsuperior properties. However, there was no concentration-dependentstabilization due to citrate buffer and it would appear that thechelating effect of citrate is not wholly responsible for thedifferential effects observed between citrate buffer and acetate buffer.

Applicants also believe that antioxidants will be useful according tothe invention. Antioxidants are substances capable of inhibitingoxidation by removing free radicals from solution. Antioxidants are wellknown to those of ordinary skill in the art and include materials suchas ascorbic acid, ascorbic acid derivatives (e.g., ascorbylpalmitate,ascorbylstearate, sodium ascorbate, calcium ascorbate, etc.), butylatedhydroxy anisole, buylated hydroxy toluene, alkylgallate, sodiummeta-bisulfate, sodium bisulfate, sodium dithionite, sodiumthioglycollic acid, sodium formaldehyde sulfoxylate, tocopherol andderivatives thereof, (d-alpha tocopherol, d-alpha tocopherol acetate,dl-alpha tocopherol acetate, d-alpha tocopherol succinate, betatocopherol, delta tocopherol, gamma tocopherol, and d-alpha tocopherolpolyoxyethylene glycol 1000 succinate) monothioglycerol, and sodiumsulfite. Such materials are typically added in ranges from 0.01 to 2.0%.

The pharmaceutical preparations of the invention also may includeisotonicity agents. This term is used in the art interchangeably withiso-osmotic agent, and is known as a compound which is added to thepharmaceutical preparation to increase the osmotic pressure to that of0.9% sodium chloride solution, which is iso-osmotic with humanextracellular fluids, such as plasma. Preferred isotonicity agents aresodium chloride, mannitol, sorbitol, lactose, dextrose and glycerol.

Optionally, the pharmaceutical preparations of the invention may furthercomprise a preservative. Suitable preservatives include but are notlimited to: chlorobutanol (0.3-0.9% WN), parabens (0.01-5.0%),thimerosal (0.004-0.2%), benzyl alcohol (0.5-5%), phenol (0.1-1.0%), andthe like.

In view of the success achieved with disodium edetate alone in anunbuffered system, it would have been expected that stable formulationscould be prepared at virtually any pH simply by optimizing the variouspotential methylnaltrexone degradation inhibiting agents. Such agentsinclude those as described above, that is, chelating agents, bufferingagents, antioxidants, and the like. It was discovered, however, thatstable formulations of methylnaltrexone in solution could not beobtained with such degradation inhibiting agents at pHs above 6. Thus,in one aspect of the invention, stable pharmaceutical preparationscontaining methylnaltrexone in solution are permitted, wherein thesolution further includes an agent selected from the group consisting ofa chelating agent, a buffering agent, an antioxidant, and combinationsthereof, provided that the solution has a pH ranging from between 2 to6.

The stable pharmaceutical preparations of the invention are stable notonly to heat degradation resulting from autoclaving, but also to othersterilization processes used during manufacturing. Sterilizationprocesses or techniques as used herein include aseptic techniques suchas one or more filtration (0.45 or 0.22 micron filters) steps,autoclaving, and a combination of filtration and autoclaving. They alsoare stable to long term storage. The stable formulations of theinvention are stable for at least six months at temperatures of 30° C.or less, preferably a range from 5° C. to 30° C., and, more preferably,they are stable at a temperature above 15° C. for at least six months.More particularly, the stable pharmaceutical preparations are stable forperiods of at least six months, at least twelve months, and even atleast twenty-four months at about room temperature or 25° C. Suchpreparations remain substantially free of methylnaltrexone degradationproducts, that is, such solutions contain less than 2% methylnaltrexonedegradation products compared to the total amount of methylnaltrexone inthe solution.

Applicants also discovered, surprisingly, that lyophilizing conditionscould dramatically affect the amount of methylnaltrexone degradationproducts. The pharmaceutical preparations of the invention therefore mayadvantageously include cryoprotective agents, which protectmethylnaltrexone from the harmful effects of freezing. Such agents alsocan prevent caking and flaking, which can be problematic inreconstituting a solution and in manufacturing processing. Importantcryoprotecting agents are mannitol, lactose, sucrose, polyethyleneglycol and polyvinyl pyrrolidine. Most preferred is mannitol. It isbelieved that cryoprotecting agents which result in a reconstitution pHof 6.0 and higher or which are basic will contribute also to degradationof methylnaltrexone due to pH effects discussed above. Thus, preferredcryoprotecting agents are those which, together with the othercomponents of the formulation, result in a Do pH in the preferred rangesdescribed above. Preferably, the cryoprotecting agent is neutral oracidic.

The amount of methylnaltrexone in the solution is effective to treatcompletely, ameliorate, or even prevent conditions associated withactivation of endogenous opioid receptors, in particular, peripheralopioid receptors such as mu opioid receptors. Such conditions includenausea, emesis, dysphoria, pruritus, urinary retention, ileus,post-operative ileus, post-partumileus, parallytic ileus, bowelhypomotility, constipation, gastric hypomotility, delayed gastricemptying, decreased biliary secretion, decreased pancreatic secretion,biliary spasm, increased sphincter tone, cutaneous flushing, impaction,sweating, inhibition of gastrointestinal motility, inhibition of gastricemptying, gastrointestinal dysfunction, incomplete evacuation, bloating,abdominal distention, increased gastroesophageal reflux, hypotension,bradycardia, irritable bowel syndrome, or immunosuppression. Oneimportant use is in the treatment of constipation, i.e., less than onebowel movement in 3 days or less than 3 bowel movements in a week.

In any of the foregoing embodiments, the methylnaltrexone can be presentin an amount sufficient to accelerate discharge from hospitalpost-surgery, accelerate bowel sounds after surgery, or induce laxation.Such amounts are well known to those of ordinary skill in the art andare described in the literature, including the patents listed in thebackground of the invention. The methylnaltrexone may also be in a saltform, including the bromide, chloride, iodide, carbonate, and sulfatesalts of methylnaltrexone.

Patients treatable with the formulations of the invention include thosereceiving opioids including opioids for pain, cancer or surgicalpatients, immunosuppressed or immunocompromised patients (including HIVinfected patients), patients with advanced medical illness, terminallyill patients, patients with neuropathies, patients with rheumatoidarthritis, patients with osteoarthritis, patients with chronic packpain, patients with spinal cord injury, patients with chronic abdominalpain, patients with chronic pancreatic pain, patients with pelvicperineal pain, patients with fibromyalgia, patients with chronic fatiguesyndrome, patients with migraine or tension headaches, patients onhemodialysis, and patients with sickle cell anemia.

The pharmaceutical preparations of the invention also can include anopioid. The therapeutic use of opioids is well known and, again, isdescribed in both the literature and the patents mentioned above.Opioids include alfentanil, anileridine, asimadoline, bremazocine,burprenorphine, butorphanol, codeine, dezocine, diacetylmorphine(heroin), dihydrocodeine, diphenoxylate, fedotozine, fentanyl,funaltrexamine, hydrocodone, hydromorphone, levallorphan, levomethadylacetate, levorphanol, loperamide, meperidine (pethidine), methadone,morphine, morphine-6-glucoronide, nalbuphine, nalorphine, opium,oxycodone, oxymorphone, pentazocine, propiram, propoxyphene,remifentanyl, sufentanil, tilidine, trimebutine, and tramadol.

It should be understood that the pharmaceutical preparations of theinvention will typically be held in bottles, vials, ampoules, infusionbags, and the like, any one of which may be sparged to eliminate oxygenor purged with nitrogen. In some embodiments, the bottles vials andampoules are opaque, such as when amber in color. Such sparging andpurging protocols are well known to those of ordinary skill in the artand should contribute to maintaining the stability of the pharmaceuticalpreparations. The pharmaceutical preparations also, in certainembodiments, are expected to be contained within syringes.

According to another aspect of the invention, kits also are provided.Referring to FIG. 3, a kit 10 is depicted. The kit 10 includes apharmaceutical preparation vial 12, a pharmaceutical preparation diluentvial 14, an opioid vial 16, and an opioid diluent vial 18. The kit alsoincludes instructions 20. The vial 14 containing the diluent for thepharmaceutical preparation is optional. The vial 14 contains a diluentsuch as physiological saline for diluting what could be a concentratedsolution of methylnaltrexone contained in vial 12. The instructions caninclude instructions for mixing a particular amount of the diluent witha particular amount of the concentrated pharmaceutical preparation,whereby a final formulation for injection or infusion is prepared. Theinstructions may include instructions for use in a patient controlledanalgesia (PCA) device. Likewise, the kit optionally contains an opioidin the opioid vial 16, which also optionally may be in a concentratedform. The optional vial 18 contains a diluent for a concentrated opioid.The instructions also may include instructions for mixing the opioidwith the pharmaceutical preparation and/or diluting the opioid with theopioid diluent contained in the opioid diluent vial 18. Theinstructions, therefore, would take a variety of forms depending on thepresence or absence of diluent and opioid. The instructions 20 caninclude instructions for treating a patient with an effective amount ofmethylnaltrexone. It also will be understood that the containerscontaining the pharmaceutical preparation, whether the container is abottle, a vial with a septum, an ampoule with a septum, an infusion bag,and the like, can contain indicia such as conventional markings whichchange color when the pharmaceutical preparation has been autoclaved orotherwise sterilized.

The pharmaceutical preparations of the invention, when used in alone orin cocktails, are administered in therapeutically effective amounts. Atherapeutically effective amount will be determined by the parametersdiscussed below; but, in any event, is that amount which establishes alevel of the drug(s) effective for treating a subject such as a humansubject, having one of the conditions described herein. An effectiveamount means that amount alone or with multiple doses, necessary todelay the onset of, inhibit completely or lessen the progression of orhalt altogether the onset or progression of the condition being treated.When administered to a subject, effective amounts will depend, ofcourse, on the particular condition being treated; the severity of thecondition; individual patient parameters including age, physicalcondition, size and weight; concurrent treatment; frequency oftreatment; and the mode of administration. These factors are well knownto those of ordinary skill in the art and can be addressed with no morethan routine experimentation. It is preferred generally that a maximumdose be used, that is, the highest safe dose according to sound medicaljudgment.

The pharmaceutical preparations of the present invention may include orbe diluted into a pharmaceutically-acceptable carrier. The term“pharmaceutically-acceptable carrier” as used herein means one or morecompatible solid, or semi-solid or liquid fillers, diluents orencapsulating substances which are suitable for administration to ahuman or other mammal such as a dog, cat, horse, cow, sheep, or goat.The term “carrier” denotes an organic or inorganic ingredient, naturalor synthetic, with which the active ingredient is combined to facilitatethe application. The carriers are capable of being commingled with thepreparations of the present invention, and with each other, in a mannersuch that there is no interaction which would substantially impair thedesired pharmaceutical efficacy or stability. Carriers suitable fororal, subcutaneous, intravenous, intramuscular, etc. formulations can befound in Remington's Pharmaceutical Sciences, Mack Publishing Company,Easton, Pa.

A variety of administration routes are available. The particular modeselected will depend of course, upon the particular drug selected, theseverity of the disease state being treated and the dosage required fortherapeutic efficacy. The methods of this invention, generally speaking,may be practiced using any mode of administration that is medicallyacceptable, meaning any mode that produces effective levels of theactive compounds without causing clinically unacceptable adverseeffects. Such modes of administration include oral, rectal, sublingual,topical, nasal, transdermal or parenteral routes. The term is“parenteral” includes subcutaneous, intravenous, intramuscular, orinfusion.

Dosage may be adjusted appropriately to achieve desired drug levels,locally or systemically. Generally, daily oral doses of active compoundswill be from about 0.1 mg/kg per day to 30 mg/kg per day. It is expectedthat IV doses in the range of 0.01-1.00 mg/kg will be effective. In theevent that the response in a subject is insufficient at such doses, evenhigher doses (or effective higher doses by a different, more localizeddelivery route) may be employed to the extent that patient tolerancepermits. Continuous IV dosing over, for example, 24 hours or multipledoses per day also are contemplated to achieve appropriate systemiclevels of compounds. Preferred subcutaneous doses for chronic opioidusers to induce laxation are 0.1-0.3 mg/kg, and preferred oral doses forthe same patient population are 1.0-3.0 mg/kg. Preferred IV doses totreat post operative ileus are 0.15 mg/kg.

The invention also involves methods for preparing autoclavedpharmaceutical preparations that have concentrations of methylnaltrexonedegradation products that do not exceed 2% of the methylnaltrexone orsalt thereof in the preparation. Aqueous solutions of methylnaltrexoneare prepared. A pH-adjusting acid is added to adjust the pH to 4.25 orless, preferably to a range of between 3.0 and 3.5. The solution is thenautoclaved according to standard procedures. One such procedure involvesautoclaving at 122° C. and 15 pounds of pressure for 20 minutes. Thepharmaceutical preparation can contain any one, any combination of orall of a chelating agent, an isotonicity agent, a buffering agent, anantioxidant, a cryoprotective agent, and an opioid. According to anotheraspect of the invention, a pharmaceutical preparation containingmethylnaltrexone in a aqueous solution is prepared by combining achelating agent with the methylnaltrexone solution and then autoclavingthe solution. The aqueous solution of methylnaltrexone may contain anyone of, any combination of or all of a buffering agent, an antioxidant,an isotonicity agent and an opioid.

According to yet another aspect of the invention, a pharmaceuticalpreparation containing methylnaltrexone in a lyophilized formulation isprepared by combining a cryoprotective agent, such as mannitol, with themethylnaltrexone formulation. The lyophilized preparation may alsocontain any one of, any combination of, or all of a buffering agent, anantioxidant, an isotonicity agent and an opioid.

The invention also involves methods of inhibiting the formation ofmethylnaltrexone degradation products in a solution containingmethylnaltrexone by combining any one of, any combination of or all of achelating agent, a buffering agent and an antioxidant withmethylnaltrexone or salt thereof in solution. In one preferredembodiment, the aqueous solution containing the chelating agent,buffering agent and/or antioxidant is first prepared, then a powderedsource of methylnaltrexone or salt thereof is dissolved into the aqueoussolution.

The invention also involves methods of inhibiting the formation ofmethylnaltrexone degradation products in a gel containingmethylnaltrexone by combining any one of, any combination of or all of achelating agent, a buffering agent and an antioxidant withmethylnaltrexone or salt thereof in a gel matrix. In one preferredembodiment, the gel containing the chelating agent, buffering agentand/or antioxidant is first prepared, then a powdered source ofmethylnaltrexone or salt thereof is dissolved into the gel. As usedherein, solution embraces gels.

The pharmaceutical preparations of the invention may be provided inparticles. Particles as used herein means nano or microparticles (or insome instances larger) which can consist in whole or in part of theperipheral opioid antagonists or the other therapeutic agent(s) asdescribed herein. The particles may contain the therapeutic agent(s) ina core surrounded by a coating, including, but not limited to, anenteric coating. The therapeutic agent(s) also may be dispersedthroughout the particles. The therapeutic agent(s) also may be adsorbedinto the particles. The particles may be of any order release kinetics,including zero order release, first order release, second order release,delayed release, sustained release, immediate release, and anycombination thereof, etc. The particle may include, in addition to thetherapeutic agent(s), any of those materials routinely used in the artof pharmacy and medicine, including, but not limited to, erodible,nonerodible, biodegradable, or nonbiodegradable material or combinationsthereof. The particles may be microcapsules which contain the antagonistin a solution or in a semi-solid state. The particles may be ofvirtually any shape.

Both non-biodegradable and biodegradable polymeric materials can be usedin the manufacture of particles for delivering the therapeutic agent(s).Such polymers may be natural or synthetic polymers. The polymer isselected based on the period of time over which release is desired.Bioadhesive polymers of particular interest include bioerodiblehydrogels described by H. S. Sawhney, C. P. Pathak and J. A. Hubell inMacromolecules, (1993) 26:581-587, the teachings of which areincorporated herein. These include polyhyaluronic acids, casein,gelatin, glutin, polyanhydrides, polyacrylic acid, alginate, chitosan,poly(methyl methacrylates), poly(ethyl methacrylates),poly(butylmethacrylate), poly(isobutyl methacrylate),poly(hexylmethacrylate), poly(isodecyl methacrylate), poly(laurylmethacrylate), poly(phenyl methacrylate), poly(methyl acrylate),poly(isopropyl acrylate), poly(isobutyl acrylate), and poly(octadecylacrylate).

The invention also provides methods for preparing stable pharmaceuticalpreparations containing aqueous solutions of methylnaltrexone or saltsthereof to inhibit formation of methylnaltrexone degradation products. Asolution is provided that contains methylnaltrexone or salts thereof andat least one methylnaltrexone inhibiting agent. The solution isprocessed under at least one sterilization technique prior to and/orafter terminal filing the solution in the sealable container to form astable pharmaceutical preparation, wherein the method is carried outwithout the addition of a pH-adjusting base to the solution.

EXAMPLES Example 1 Manufacturing Process for a PharmaceuticalFormulation of Methylnaltrexone

A manufacturing process can be outlined as follows:

-   -   1. Add required amount of water for injection (˜80% or final        volume) to a stainless steel tank.    -   2. Add chelating agent to the tank and stir till dissolved.    -   3. Add buffering agent to the tank and stir till dissolved.    -   4. Add methylnaltrexone to the tank and stir till dissolved.    -   5. Add isotonicity agent to the tank and stir till dissolved.    -   6. Adjust the pH of the solution to pH 3.25.    -   7. Add water for injection to increase the volume to the        required amount.    -   8. Transfer material to supply pressure vessel.    -   9. Sterile filter into a sterile stainless steel pressure        vessel.    -   10. Fill into bottles/vials, purge with nitrogen and then        stopper the bottles/vials.    -   11. Sterilize the filled vials by autoclaving.        Exact Amount of Excipients to be Used:

Disodium edetate = 0.75 mg/ml Added in step 2 Sodium Citrate = 0.199mg/ml Added in step 3 Citric acid = 0.35 mg/ml Added in step 3 SodiumChloride = 8.5 mg/ml Added in step 5

The order of addition of excipients is described above. Steps 2 to 5 cantake place in any order.

When all excipients and drug have been added, step 6, pH of the solutionis adjusted by addition of acid. If a buffering agent is used in thesolution, pH adjustment may not be required.

There are no specifics on the temperature or the stirring speed duringthe formulation. The temperature during formulation can be as high as80° C.

Example 2 Preferred Manufacturing Process for a PharmaceuticalFormulation of Methylnaltrexone

A preferred manufacturing process is as follows:

100 ml of 20 mg/ml solution of methylnaltrexone solutions

-   1. Add 80 ml of water for injection (˜80% or final volume) to a    stainless steel tank.-   2. Add 75 mg of disodium edetate, a chelating agent, to the tank and    stir till dissolved.-   3. Add 19.9 mg of sodium citrate and 35 mg of citric acid (as    buffering agents) to the tank and stir till dissolved.-   4. Add 2000 mg of methylnaltrexone to the tank and stir till    dissolved.-   5. Add 850 mg of sodium chloride, an isotonicity agent, to the tank    and stir till dissolved.-   6. Adjust the pH of the solution if necessary.-   7. Add water for injection to increase the volume to 100 ml.-   8. Transfer the material to supply pressure vessel.-   9. Sterile filter using a 0.22 micron filter into a sterile    stainless steel pressure vessel.-   10. Fill, purge with nitrogen and then stopper the bottles/vials.-   11. Sterilize the filled vials by autoclaving.

Example 3 12 Month Stability of Pharmaceutical PreparationMethylnaltrexone

Methylnaltrexone (bromide salt) and its degradation products in anisotonic saline solution were tested upon manufacture of the solution(no added stabilizers, sterile filtered, not autoclaved) and uponstorage at room temperature for 12 months using a Hewlett-Packard HP1100series, HPLC system equipped with quaternary gradient pump, programmablevariable wavelength UV detector and a Millennium data acquisitionsystem. Two mobile phases were prepared as follows:

The reagents, standards and media included naltrexone methobromide as areference standard, trifluoroacetic acid (ACS grade), acetonitrile (HPLCgrade), Milli-Q water (or equivalent), and methanol (HPLC grade). Thesolutions were prepared as follows. Mobile phase A (85:15:0.1)(water:methanol:trifluoroacetic acid): 850 mL of Milli-Q water was addedto a suitable container, to which 150 mL of methanol and 1.0 mL oftrifluoroacetic acid were added. The solution was mixed well and allowedto equilibrate to room temperature. The solution was degassed by heliumsparge. Mobile phase B (methanol): Methanol was added to a suitablecontainer and degas sed by helium sparge.

Instrumental Conditions

Analytical Column: Metachem Inertsil ODS3, 5 μm, 150×4.6 mm orequivalent

Mobile phase: A mixture of Mobile phase A and B is used as shown inTable I:

TABLE I Time (minutes) % A % B 0 100 0 12 65 35 15 35 65 15.1 100 0 20100 0

-   Column temperature: 50° C.-   Detection: UV at 280 nm-   Injection volume: 20 μL-   Run time: 20 minutes-   Flow rate: 1.5 mL/minute-   Quantitation: Peak area responses    Results:-   20 mg/ml saline drug product lot CTM-02085

Initial 12 months Peak % % No. RRT Degradants RRT Degradants 1degradation product 0.72 0.07 0.74 0.25 2 degradation product 0.89 <0.050.89 0.72 3 methylnaltrexone 1.00 99.7 1.00 98.6 4 degradation product1.48 0.06 1.40 0.16 5 O-Methylnaltrexone 1.57* 0.17 1.54* 0.17 Bromide(process impurity)

Samples from the methylnaltrexone saline formulation (not autoclaved)were analyzed for methylnaltrexone degradation products before and afterstorage for 12 months at 25° C.

The starting material was analyzed by HPLC. As shown in FIG. 1,methylnaltrexone is a peak having an RRT of 1.0 (4.364 minutes). Anadditional peak was identified as O-methyl naltrexone methobromide, RRTabout 1.57 (6.868 minutes). The O-methyl-naltrexone is not a degradantof methylnaltrexone but a result from the methylnaltrexone (drugsubstance) manufacturing process.

The material stored for 12 months was similarly analyzed by HPLC. Thechromatogram is shown in FIG. 2.

As in the starting material, the HPLC analysis of the sample stored for12 months showed methylnaltrexone RRT of 1.00 (3.839 minutes),O-methyl-methylnaltrexone RRT of about 1.53 (5.866 minutes). However,HPLC analysis revealed that the methylnaltrexone saline formulationwhich was stored for 12 months had at least three degradation productsformed during the manufacturing or during storage of the finished drugproduct. The degradant peak RRT's were approximately 0.74 (2.828minutes), 0.89 (3.435 minutes) and 1.40 (5.326 minutes).

HPLC analysis was also conducted, prior to storage, on amethylnaltrexone solution manufactured using an isotonic saline solution(no added stabilizers), sterile filtered, and autoclaved. This saline,autoclaved solution contained the degradation products formed duringmanufacturing or storage, as described above (data not shown).

Example 4 Preparation of a Subcutaneous Formulation

The degradation products seen with very low citrate level were the sameas those seen with normal saline solution. These low citrate formulaswere autoclaved and after three months the amount of degradationproducts seen were less than 0.1% for each degradation product. Theformula used for the citrate/EDTA formulation is listed below:

mg/mL Methynaltrexone 30 mg Sodium Chloride 4 mg Citric acid 0.0875 mgTrisodium Citrate 0.0496 mg Disodium edetate 0.75 mg Water for injectionq.s. to 1 gramThe pH of this solution is 3.5 and can withstand autoclaving process.

Example 5 Manufacturing Process for a Lyophilized PharmaceuticalFormulation of Methylnaltrexone

The lyophilization cycle listed below is standard procude well known toone of ordinary skill in the art. This cycle was used for thepreparation of lyophilized preparation of methylnaltrexone analyzed inExamples 6 and 7.

-   1. Load chamber at room temperature (20-25 C)-   2. Lower shelf temp to −45 degrees C. at 1.0 degrees C/min-   3. Hold shelf temp at −45 for 120 minutes-   4. When condenser is below −50 degrees C., evacuate the chamber to    100-125 mt.-   5. Ramp shelf to −20 degrees C. at 0.5 degrees C/min.-   6. Hold at −20 degrees C. for 16 hours-   7. Ramp shelf to +27 degrees C. at 0.10 degrees C/min-   8. Hold for a minimum of 8 hours. Maintain chamber pressure at    100-125 mt for the entire cycle.-   9. Restore chamber to 11.0 PSIA + or −1.0 with sterile filtered    Nitrogen and then seat the closures (2″ Hg), then bleed to    atmospheric pressure with Nitrogen to unload.

Example 6 Stability of Lyophilized Formulations of Methylnaltrexone

The following data reports the stability of lyophilized formulations ofmethylnaltrexone using different cryoprotecting agents.

total degradation Cryoprotecting Agent pH products Mannitol 5.0 0.34%Polyvinyl pyrrolidone 4.1 0.37% Polyethylene glycol 5.7 0.44% Histidine7.4 0.55%

Example 7 Stability of Lyophilized Formulations of Methylnaltrexone

The following data reports the stability of lyophilized formulations ofmethylnaltrexone in comparison to buffered formulations.

Amount of Total Related Substances at Various Stages of Manufacturing

1 2 3 4 5 6 Key Monothio- Citrate Citrate Acetate Lyoph- Lyoph-Ingredient glycerol Buffer Buffer Buffer ilized ilized pH 3.5 pH 5 pH3.6 using using Mannitol Lactose Unauto- 0.13 0.12 0.16 0.20 0.14 0.12claved Auto- 0.91 0.23 0.61 1.39 n/a n/a claved Stability 1.10 0.16 0.481.26 0.15 0.15 (2 mths at room temp)

It should be understood that various changes and modifications to thepreferred embodiments described herein will be apparent to those ofordinary skill in the art. Such changes and modifications can be madewithout departing from the spirit and scope of this invention withoutdiminishing its advantages. It is therefore intended that such changesand modifications, including equivalents, be covered by the appendedclaims. All of the patents, patent applications and references listedherein are incorporated by reference in their entirety.

We claim:
 1. A stable pharmaceutical preparation comprising a solution of methylnaltrexone or salt thereof and a chelating agent consisting of EDTA, or a derivative thereof, wherein the solution has a pH ranging from about 3.0 to 4.0.
 2. The pharmaceutical preparation of claim 1, wherein less than 1% methylnaltrexone degradation products form following 12 months stored at about room temperature, relative to the total methylnaltrexone present in the solution.
 3. The pharmaceutical preparation of claim 1, wherein less than 1% methylnaltrexone degradation products form following 24 months stored at about room temperature, relative to the total methylnaltrexone present in the solution.
 4. The pharmaceutical preparation of claim 3, wherein the concentration of methylnaltrexone or salt thereof ranges from 0.01 to 100 mg/ml.
 5. The pharmaceutical preparation of claim 4, wherein the concentration of methylnaltrexone or salt thereof ranges from 1.0 to 50.0 mg/ml.
 6. The pharmaceutical preparation of claim 5, wherein the concentration of methylnaltrexone or salt thereof is about 20 mg/ml.
 7. The pharmaceutical preparation of claim 5, wherein the chelating agent consists of dipotassium edetate, disodium edetate, edetate calcium disodium, sodium edetate, trisodium edetate, potassium edetate, or a combination thereof.
 8. The pharmaceutical preparation of claim 7, wherein the chelating agent consists of edetate calcium disodium.
 9. The pharmaceutical preparation of claim 8, wherein the chelating agent concentration ranges from about 0.001 to about 100 mg/ml.
 10. The pharmaceutical preparation of claim 9, wherein the chelating agent concentration ranges from about 0.1 to about 25.0 mg/ml.
 11. The pharmaceutical preparation of claim 10, wherein the chelating agent concentration is about 0.1 to about 2.5 mg/ml.
 12. The pharmaceutical preparation of claim 5, further comprising an isotonicity agent.
 13. The pharmaceutical preparation of claim 7, further comprising an isotonicity agent.
 14. The pharmaceutical preparation of claim 8, further comprising an isotonicity agent.
 15. The pharmaceutical preparation of claim 5, wherein the preparation comprises a buffering agent.
 16. The pharmaceutical preparation of claim 7, wherein the preparation comprises a buffering agent.
 17. The pharmaceutical preparation of claim 8, wherein the preparation comprises a buffering agent.
 18. The pharmaceutical preparation of claim 7, further comprising a preservative and an isotonicity agent.
 19. The pharmaceutical preparation of claim 18, wherein the preparation comprises a buffering agent.
 20. The pharmaceutical preparation of claim 1, wherein the preparation comprises a solution of methylnaltrexone bromide.
 21. The pharmaceutical preparation of claim 1, wherein less than 2% methylnaltrexone degradation products form following 12 months stored at about room temperature, relative to the total methylnaltrexone present in the solution.
 22. The pharmaceutical preparation of claim 1, wherein the preparation is processed under at least one sterilization technique.
 23. The pharmaceutical preparation of claim 1, wherein the solution has a pH from about 3.0 to about 3.5.
 24. The pharmaceutical preparation of claim 1, wherein the solution has a pH of about 3.5.
 25. A stable pharmaceutical preparation comprising a solution of methylnaltrexone or salt thereof, EDTA or a derivative thereof, wherein the solution has a pH from about 3.0 to 4.0, and wherein the methylnaltrexone or salt thereof is the sole pharmaceutical active agent.
 26. The stable pharmaceutical preparation of claim 25, wherein the solution has a pH ranging from about 3 to about 3.5.
 27. The stable pharmaceutical preparation of claim 26, wherein the solution has a pH of about 3.5.
 28. The pharmaceutical preparation of claim 25, wherein the pharmaceutical preparation is stable to storage for 3 months at about room temperature.
 29. The pharmaceutical preparation of claim 26, wherein the pharmaceutical preparation is stable to storage for 6 months at about room temperature.
 30. The pharmaceutical preparation of claim 26, wherein the pharmaceutical preparation is stable to storage for 12 months at about room temperature.
 31. The pharmaceutical preparation of claim 26, wherein the pharmaceutical preparation is stable to storage for 24 months at about room temperature.
 32. The pharmaceutical preparation of claim 26, wherein the concentration of methylnaltrexone or salt thereof is about 20 mg/ml.
 33. The pharmaceutical preparation of claim 32, wherein the concentration of EDTA or derivative thereof ranges from about 0.3 to about 0.5 mg/ml.
 34. The pharmaceutical preparation of claim 25, wherein about 1% or less methylnaltrexone degradation products form following 3 months stored at about room temperature, relative to the total methylnaltrexone present in the solution.
 35. The pharmaceutical preparation of claim 27, wherein about 1% or less methylnaltrexone degradation products form following 6 months stored at about room temperature, relative to the total methylnaltrexone present in the solution.
 36. The pharmaceutical preparation of claim 27, wherein about 1% or less methylnaltrexone degradation products form following 12 months stored at about room temperature, relative to the total methylnaltrexone present in the solution.
 37. The pharmaceutical preparation of claim 27, wherein about 1% or less methylnaltrexone degradation products form following 24 months stored at about room temperature, relative to the total methylnaltrexone present in the solution.
 38. The stable pharmaceutical preparation of claim 25, wherein the methylnaltrexone or salt thereof is methylnaltrexone bromide and is at a concentration of about 20 mg/mL, wherein the EDTA or a derivative thereof is at a concentration of about 0.3 to about 0.5 mg/ml, wherein the solution has a pH of about 3.5.
 39. The stable pharmaceutical preparation of claim 38, wherein about 1% or less methylnaltrexone degradation products form following 3 months stored at about room temperature, relative to the total methylnaltrexone present in the solution. 